President Donald Trump warned yesterday that it is now or never when it comes to extending protections for young immigrants, while Senate Majority Leader Mitch McConnell threw his weight behind legislation based on the president's priorities.

Trump, in an early-morning tweet, said Congress must act now to provide legal protections to young 'Dreamer' immigrants even as legislation faces an uncertain prospect in Congress.

"Wouldn't it be great if we could finally, after so many years, solve the DACA puzzle," he wrote, adding: "This will be our last chance, there will never be another opportunity! March 5th."

Trump was referring to a deadline he announced last year to end a programme protecting young immigrants from deportation. But a recent court ruling has rendered that deadline all but meaningless.

The comments came the day after the Senate voted 97-1 Ted Cruz, R-Texas, provided the sole 'no' vote to plunge into an open-ended immigration debate that's been promised by McConnell. Both parties' leaders hope debate can be concluded this week, but it's unclear if that will happen or what the product, if any, will be.

One GOP proposal would pave a path to citizenship for up to 1.8 million young 'Dreamer' immigrants in the US, a lure for Democrats that many Republicans oppose.

McConnell and other GOP supporters describe the measure as the Senate's best shot of passing a bill that the president will sign, but many Democrats consider some of the proposals, including limiting the relatives that legal immigrants can bring to the US, to be non-starters.